I don't think this would be good idea. Then there would be the danger of employers pressuring their employees to waive their rights: "If you insist on working

I don't think this would be good idea. Then there would be the danger of employers pressuring their employees to waive their rights: "If you insist on working only 11h/day, we can hire someone else." I would totally expect this to happen for basically every minimum wage job if you could waive your rights like this.